Process of hardening gelatin and photographic gelatin emulsions



Patented Feb. 19, 1952 PROCESS OF HARDENIN G GELATIN AND PHOTOGRAPHIC GELATIN EMULSIONS Frank .J. Kaszuba, Binghamton, N. Y., assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application July 11, 1947,

. Serial No. 760,488

Claims.

This invention relates to the hardening of gelatin, and especiallyto the hardening of photographic gelatin and gelatino silver-halide emulsions to yield compositions having an appreciable increase in melting point and good stability on ageing with respect to fog, speed, and gradation.

In the preparation of photographic gelatin dispersions and gelatino silver-halide emulsions, it has been the practice to treat the dispersions and emulsions, prior to coating, with a hardening agent so as to reduce the tendency of the gelatin to soften, or to 'distend during processing of the photographic material containing the gelatin, particularly at temperatures higher than the temperature specified for processing the particular photographic material. Compounds which have been used for hardening gelatin as such or in silver-halide emulsions are formaldehyde, hydroxy aldehydes, acrolein, glyoxal, and derivatives thereof, and mixtures of an aliphatic aldehyde with an aromatic compound containing at least one nuclear hydroxy substituent group such as phenol, resorcinol, resorcyclic aldehyde, and the like. Although formaldehyde and hydroxy aldehydes are satisfactory as hardening agents, these compounds possess the undesirable property of producing excessive fog, desensitization, or flattening of gradation in the processed film. Any hardeners that function by the liberation of formaldehyde will also-have these deleterious effects as well as that of after-harden-- ing. Aliphatic aldehydes, with an aromatic compound containing at least one nuclear hydroxy substituent group, induce some increase in the melting point. They fail, however, to give both an appreciable increase in the melting point and good stability upon ageing in respect to fog, speed, and gradation.

In U. S. Patent 2,354,662, nitrogenous methylol derivatives such as methylol ureas, thioureas, guanidines, and the like, are suggested as hard-. eners for gelatin. The specification of this application explains that the tanning action is actually the function of the formaldehyde liberated when these compounds are heated. The employment of these compounds, coupled with heating them, will have a deleterious efiect on the photographic properties of the emulsion, especially when of a high speed type.

In U. 6. Patent 2,165,421, it is suggested that the stability of emulsions hardened by formaldehyde, and other aldehydes, can be improved by the use of hydroxy-benzenes, such as resorcinol, phloroglucinol, resorcylic aldehyde, and the like.

2 However, even though this treatment does lead to some improvement in the stability of the photographic properties on ageing, it is not entirely adequate, especially with high speed emulsions. In other words, although aliphatic aldehydes with hydroxy-benzenes induce an increase in the melting point, they invariably cause lossin speed and gradation so that one has to make compromises between hardening and speed. Moreover, by the use of such a combination, only relatively :little hardening can be achieved without causing deleterious effects in the photographic characteristics of the emulsion.

It is an object of the present invention to provide a photographic gelatin or a gelatino silver-halide emulsion having an appreciable higher melting point and much better stability on ageing thangelatin or gelatino silver-halide emulsions per se.

Another object is to provide gelatin layers and gelatino silver-halide emulsion layers in which the gelatin is not subject to the phenomenon known as after-hardening.

A further object is to provide a gelatino silverhalide emulsion which will not fog on storage.

A still further object is to provide a gelatino silver-halide emulsion which will be resistant to relatively high processing temperatures without fogging, loss of speed, and loss of gradation.

Other objects will appear hereinafter.

The foregoing objects are accomplished, according to the present invention, by incorporating into the gelatin or gelatino silver-halide emulsion, a dimethyl'ol-diketopiperazine, with or without other compounds which alone possess little or no hardening effect upon gelatin or gelatino silver-halide emulsions, but in conjunc- The dimethylol-diketopiperazines, which may be utilized, are characterized by a structure corresponding to the following general formula:

wherein R represents either hydrogen or an alkyl group of not more than 4 carbon atoms, e. g.,

O PJCH HOCHz-N N-CHzOH 1,4-dimethylol-2,5-diketopiperazine lA-dimethylol-3,6-dimethyl-2,5-diketoplperazine CHa-l-CH; H

1,4-dimethylol-3,6-di-isopropyl-2,E-diketopiperazine 1,4-dimethylol-3,6-di-isobutyl-2,5-diketopiperazine 1.4-dimethylol-3,6-diphenyl-2,5diketopiperazine The foregoing compounds are prepared by the methods disclosed in Beil. 24, 264; 297; 308 and 413; Ber. 34, 2870 and 39, 2931; and Helv. Chim. Acta. 5, 683 (1922). The latter reference discloses the reaction of diketopiperazine with formaldehyde to give the dimethylol derivatives.

The compounds, which alone possess little or no hardening effect on gelatin or gelatino silverhalide emulsions, and which may be added in conjunction with the dimethylol-diketopiperazine, are 2,4-dihydroxy benzaldehyde (resorcylic aldehyde) and 1,3-benzenediol (resorcinol).

The function of 2,4-dihydroxy benzaldehyde in the mixture is to boost or accelerate the hardening action of the dimethylol-diketopiperazine. When resorcinol is added to this combination, the optimum in hardening as well as in photographic properties is obtained. A very desirable increase in melting point of gelatin or gelatino silver-halide emulsions is obtained by the utilization of dimethylol-diketopiperazines alone, said increase in melting point being unaccompanied by any tendency for the gelatin or emulsion to undergo the phenomenon of after-hardening. 7

If with the dimethylol-diketopiperazines there be added 2,4-dihydroxy benzaldehyde, greater hardness is obtained, the 2,4-dihydroxy benzaldehyde operating as it were to accelerate the hardness attributable to the dimethylol-diketopiperazines.

The results obtained with the dimethylol-diketopiperazines in admixture with the 2,4-dihydroxy benzaldehyde are greatly improved if there also be employed resorcinol. This compound does not detract in the slightest from the hardening effect obtained with the other components, and, rather surprisingly in cooperation with said other ingredients, confers upon the final sensitized emulsions a very excellent stability on ageing with respect to fog, speed and gradation. While, therefore, the invention contemplates the utilization of the dimethylol-diketopiperazines alone to eflect hardening while avoiding the phenomenon of after-hardening, it likewise contemplates the employment with the dimethylol-diketopiperazines of 2,4-dihydroxy benzaldehyde and resorcinol either alone or together. Inasmuch as best results are obtained when all three components are employed, the use of the same represents the preferred embodiment of the invention.

It is to be noted that from the large class of dihydroxy benzaldehydes, 2,4-dihydroxy benzaldehyde is the only one to accelerate the hardening effect of the dimethylol-diketopiperazines without impairing the photographic characteristics of the emulsions, and from the large class of aromatic hydroxy compounds containing at least 1 nuclear hydroxy group, resorcinol was found to be the only one, when in an admixture with a dimethylol-diketopiperazine and 2,4-dihydroxy benzaldehyde, to act as a stabilizing agent so as to impart excellent additional stability to the emulsion with respect to fog, speed, and gradation.

I Where it is desired to increase the melting point of the gelatin in a gelatin dispersion utilized in the preparation of non-curling layers, filter and anti-halation layers, or anti-abrasion layers, a sufficient quantity of the dimethyloldiketopiperazine alone is added. While the exact amount of the dimethylol-diketopiperazine may be varied within wide limits and with due regard to the particular type of gelatin dispersion employed, in general, amounts ranging from 0.05% to 2.5% based on the dry weight of gelatin in the dispersion are preferred. In these amounts, effective hardening is obtained without after-hardening, i. e., the melting point of the gelatin does not vary with time or with long periods of storage prior to actual use and. processing of the photographic material provided with such a layer.

In cases, especially in anti-abrasion layers, where the optimum in hardness is desired, a mixture of the dimethylol-diketopiperazine and 2,4-dihydroxy benzaldehyde is employed. The amount of 2,4-dihydroxy benzaldehyde to be added may vary from 0.005% to 2.5% based on the dry Weight of gelatin.

In hardening gelatin emulsions which are slightly alkaline, i. e., emulsions having a pH greater than '7, generally between '7 and 8.5, the exact amounts of the dimethylol-diketopiperazine, 2,4-dihydroxy benzaldehyde, and resorcinol may also be varied within wide limits depending largely upon the desired degree of hardening, stabilizing effect, and gradation. In general, the

v amounts of the dimethylol-diketopiperazine may 0 vary from 1 to 5 parts by weight, the amount of 2,4-dihydroxy benzaldehyde may vary from 0.1 to 5 parts by weight, and the amount of resorcinol may vary from 1 to 10 parts by weight per 10 kilogram of emulsion containing 840% gelatin.

Where it is desired to increase the speed and aces-nee:

gradation of a silyenhalide emulsion, I prefer to use resorcinol inconjunction with the. .dimethylolr' diketopiperazine and. 2,4-dihydroxy benzaldehyde. It is to be understood, however, that these emulsions may also be hardened by mixing therewith prior to coating the dimethylolediketopiperazine alone or in combination with 2,4-dihydroxy benzaldehyde. In the latter case the melting point of the gelatin rises appreciably without the attendant serious loss of photographic characteristics.

' While the following examples describein detail the methods for accomplishing the aforestated objects, it is to be understood that they are given merely for the purpose of illustration and are not to be construed as limiting the scope of the invention.

EXAMPLE I EXAMPLE II Example I was repeated with the exception that 40 mls. of 1,4-dimethylol-3,6-dimethyl-2,5- diketopiperazine was substituted for 40 mls. of lA-dimethylol-2,5-diketopiperazine. The results obtained were practically identical with those of Example I.

EXAMPLE III Example I was again repeated with the exception that 40 mls. of 1,4-dimethylol-3,6diisopropyl-2,5-diketopiperazine was substituted for 40 mls. of 1,4-dimethylol-2,5-diketopiperazine. The

results obtained were practically identical with those of Example I.

EXAMPLE IV To a liter of a photographic silver-halide emulsion, containing 8-10% aqueous gelatin and melting at C., mls. of a 0.25% aqueous solution of 1,4-dimethylol-2,5-diketopiperazine and 40 mls. each of a 1.25% aqueous solution of 2,4-dihydroxy benzaldehyde and resorcinol were added at a temperature of40 C. A glass plate was coated with a thin layer of this emulsion and dried at room temperature. The emulsion layer melted at 49 C., and the film was tougher than the film of Example I. After ageing for 18 days, the melting point was substantially unchanged. Similar stability on ageing was obtained with respect to photographic characteristics.

EXAMPLE V X -ray emulsion Quantity of 1,4dimethylol-3,6-dimethyl-2,5-diketopiperazine 0 0.27 Quantity of 2,4 dihydroxybenzaldehyde 0 a 0.14

Quantity of resorcinol r \0- 1.21

Fog 0:20 .15

Speed 158 198 Gradation 0.75 0.80. EXAMPLE'VI This example shows the effect on fog in a silver-halide emulsion containing 8-10% of gelatin by a mixture of 1,4-dimethylol-3,6-di-isopropyl-2,5diketopiperazine, 2,4-dihydroxy benzaldehyde, and resorcinol. All parts are in per cent based on the dry weight of the gelatin in the emulsion.

From the foregoing examples, it is clearly apparent that my invention is not only applicable to the preparation of photographic silver-halide emulsions of satisfactory hardening properties, but also to the preparation of gelatin dispersions and dispersions of gelatin substitutes, which are normally capable of being hardened with formaldehyde, especially those which are and have been used in the preparation of various coatings or layers on paper, cloth, film, glass, and other surfaces.

I claim:

1. The method of producing a hardened gelatin layer in a photographic silver-halide element having no after-hardening tendency'which comprises uniformly mixing therewith, prior to coating upon a support, a dimethylol-diketopiperazine hardening agent characterized by the following general formula:

3. The method of producing a hardened gelatin layer in a photographic silver-halide element having no after-hardening tendency which comprises uniformly mixing therewith, prior to coating upon a support, a dimethylol-diketopiperazine hardening agent of the-following formula:

1,4-Dimethylol-3,6-di- 24 d isopropyl-2 ,5-diketo- 1 y roxy. Resorcinol F0 Value piperazme benzaldehyde g 4.. The'method of producing a hardened gelatin layer in a photographic silver-ahalide element having no after-hardening tendency which comprises uniformly mixing therewith, prior to coating upon a support, a dimethylol-diketopiperazine hardening agent of the following formula:

5. The method of producing a hardened gelatin layer in a photographic silver-halide element having no after-hardening tendency which comprises uniformly mixing therewith, prior to coating upon a support, 2,4-dihydroxy benzaldehyde and a dimethylol-diketopiperazine hardening agent characterized by the following general formula:

wherein R represents a member selected from the class consisting of hydrogen, and an alkyl group of not more than 4 carbon atoms and a phenyl group.

6. The method of producing a hardened gelatin layer in a photographic silver-halide element having no after-hardening tendency which comprises uniformly mixing therewith, prior to coating upon a support, 2,4-dihydroxy benzaldehyde, resorcinol, and a dimethylol-diketopiperazine hardening agent characterized by the following general formula:

wherein R represents a member selected from the classconsisting of hydrogen, and an alkyl group of not more than 4 carbon atoms and a phenyl group.

7. The method of producing a hardened gelatin layer in a photographic silver-halide element having no after-hardening tendency which comprises uniformly mixing therewith, prior to coating upon a support, ZA-dihydroxy benzaldehyde, resorcinol, and a dimethylol-diketopiperazine hardening agent of the following formula:

N-CHIOH f? -4311, noom-N -OH2OH 8. The method of producing a hardened gelatin layer in a photographic silver-halide element having no after-hardening tendency which comprises uniformly mixing therewith, prior to coating upon a support, 2,4-dihydroxy benzaldehyde,

resorcinol, and a dimethylol-diketopiperazine hardening agent of the following formula:' I

9. The method of producing a hardened gelatin layer in a photographic silver-halide element having no after-hardening tendency which comprises uniformly mixing therewith, prior to coating upon a support, 2,4-dihydroxy benzaldehyde, resorcinol, and a dimethylol-diketopiperazine hardening agent of the following formula:

HocHr-N NCHzOH i i H of; CHa 10. A photo-sensitive element comprising a support and a gelatin silver-halide emulsion coated thereon, said emulsion containing as hardening means a dimethylol-diketopiperazine characterized by the following general formula:

wherein R represents a member selected from the class consisting of hydrogen, and an alkyl group of not more than 4 carbon atoms and a phenyl group.

11. A photo-sensitive element, comprising a support and a gelatin silver-halide emulsion coated thereon, said emulsion containing as hardening means 2,4-dihydroxy benzaldehyde and a dimethylol-diketopiperazine characterized by the following general formula:

( R tH Nom011 oH-o R 1% wherein R represents a member selected from the class consisting of hydrogen, and an alkyl group of not more than 4 carbon atoms and a phenyl group.

CH2OH 13. A photo-sensitive element, comprising a support and a gelatin silver-halide emulsion coated thereon, said emulsion containing as hardening means a mixture of 2,4-dihydroxy benzaldehyde, resorcinol, and a dimethylol-diketopiperazine of the following formula:

en, t

15. A photo-sensitive element, comprising a support and a gelatin silver-halide emulsion coated thereon, said emulsion containing as hardening means a mixture of 2,4-dihydroxy benzalde- 10 hyde, resorcinol, and a dimethylol-diketopiperazine of the following formula:

H O CHz-N o o C CHa FRANK J. KASZUBA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,165,421 Sheppard et a1 July 11, 1939 2,422,680 Jennings June 24, 1947 OTHER REFERENCES The Theory of the Photographic Process, Mees. publ. by the Macmillan 00., 1942, pages 123-126.

Sheppard: Gelatin in Photography, published by D. Van Nostrand Company, New York, 1923, volume 1, page 151. 

1. THE METHOD OF PRODUCING A HARDENED GELATIN LAYER IN A PHOTOGRAPHIC SILVER-HALIDE ELEMENT HAVING NO AFTER-HARDENING TENDENCY WHICH COMPRISES UNIFORMLY MIXING THEREWITH, PRIOR TO COATING UPON A SUPPORT, A DIMETHYLOL-DIKETOPIPERAZINE HARDENING AGENT CHARACTERIZED BY THE FOLLOWING GENREAL FORMULA:
 5. THE METHOD OF PRODUCING A HARDENED GELATIN LAYER IN A PHOTOGRAPHIC SILVER-HALIDE ELEMENT HAVING NO AFTER-HARDENING TENDENCY WHICH COMPRISES UNIFORMLY MIXING THEREWITH, PRIOR TO COATING UPON A SUPPORT, 2,4-DIHYDROXY BENZALDEHYDE AND A DIMETHYLOL-DIKETOPIPERAZINE HARDENING AGENT CHARACTERIZED BY THE FOLLOWING GENERAL FORMULA: 